As one of the cleaning methods of the semiconductor wafer, it has been carried out a cleaning treatment by using ozonated water, diluted hydrofluoric acid, and pure water in combination. As a general flow of the cleaning in this case, the cleaning is carried out in the order of ozonated water cleaning→diluted hydrofluoric acid cleaning→ozonated water (pure water) cleaning→drying.
In this method, an organic material(s) attached to a surface of the semiconductor wafer is removed by the first ozonated water cleaning, an oxide film formed on the surface of the semiconductor wafer and metal impurities incorporated into the oxide film are simultaneously removed in the next diluted hydrofluoric acid cleaning, thereafter, when a protective oxide film is necessary for the surface of the semiconductor wafer, surface oxidation treatment by ozonated water (or pure water) is carried out. Also, for the purpose of improving a cleaning power, it has been practiced a method in which formation and etching of an oxide film on the surface of the semiconductor wafer are repeated by ozonated water and hydrofluoric acid (Patent Document 1).
For example, in the cleaning of a semiconductor wafer by a single wafer processing spin cleaning, ozonated water cleaning, HF (hydrofluoric acid) cleaning, and pure water cleaning are carried out in combination as mentioned above, and in the HF cleaning carried out after formation of an oxide film on the surface of a semiconductor wafer by the ozonated water cleaning, the oxide film itself is removed simultaneously with the metal impurities incorporated into the oxide film. According to this procedure, a surface (hereinafter referred to bare surface) in which oxide film is not formed is exposed at the surface of the semiconductor wafer, whereby the surface becomes the state in which particles are likely adhered and a particle level is degraded. Therefore, in the cleaning of a semiconductor wafer, it is the problem to reduce the metal impurity level and the particle level simultaneously.